2.9.4Inquiry Process
Abiotic Factors- Marine and Terrestrial — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 95 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Coral Reef Formation
Reef-building corals show how several abiotic factors together set a distribution.
Coral partnership
- Coral partnership A coral polyp lives in symbiosis with zooxanthellae, algae that photosynthesise and supply carbon compounds while the polyp provides shelter.
Reef building
- Reef building Many polyps secrete calcium carbonate, which accumulates in layers over thousands of years to form the hard structure of a reef.
Limited range
- Limited range Reef-building corals are restricted to tropical and subtropical seas because they have a narrow range of tolerance for several abiotic factors.
Non-reef corals
- Non-reef corals Coral species that do not build reefs can live in other regions, including cooler water, so the restriction applies to reef builders.
Part 2 of 4Abiotic Limits on Reefs
Water depth
- Water depth Reefs grow in shallow water where enough light penetrates for the zooxanthellae to carry out photosynthesis.
pH
- pH Calcium carbonate dissolves in acidic water, and hydrogen ions combine with carbonate ions, so low pH reduces the carbonate available for building.
Salinity
- Salinity Corals are marine animals that need salt water, roughly 32 to 42 parts per thousand, so fresh water run-off can limit growth.
Water clarity
- Water clarity Sediment and pollution cloud the water and reduce the light reaching the algae, which limits coral growth.
Temperature
- Temperature Corals tolerate about 20 to 28 °C and grow best above about 23 °C;
- warming makes polyps expel their algae, which causes bleaching.
| Factor | Why it limits coral | Human influence |
|---|---|---|
| pH | Carbonate needed for skeleton | Dissolved CO₂ from fossil fuels |
| Salinity | Marine animals need salt water | Freshwater run-off |
| Clarity | Light needed by algae | Sediment and pollution |
| Temperature | Narrow tolerance | Rising sea temperature |
Part 3 of 4Biomes and the Climograph
Biomes and the Climograph
Biome
- Biome A large community of plants and animals formed over a wide area as a result of environmental factors, usually named after the dominant vegetation.
Examples
- Examples Tropical rainforest, temperate deciduous forest, boreal forest or taiga, grassland, tundra and desert are common examples.
Climograph
- Climograph A graph of mean annual rainfall against mean annual temperature that shows which biome is expected for each combination.
Reading it
- Reading it For about 100 cm of rain and a mean temperature of 0 °C the climograph indicates taiga,
- whereas 300 cm and 15 °C gives temperate rainforest.
Limitations
- Limitations Boundaries between biomes are gradual in reality, and soil type or grazing can also change the biome that develops.
Part 4 of 4Exam Checklist & Tips
2.9.4 – Key Points for the Exam
- Zooxanthellae Photosynthetic algae that live inside coral polyps in a symbiotic relationship.
- Coral bleaching Loss of algae from coral tissue, often caused by raised water temperature.
- Biome A large community of plants and animals that develops because of environmental factors.
- Climograph A graph of rainfall against temperature used to predict the biome of a region.
Common Mistakes
- Saying all corals are limited to the tropics; only reef-building species have this restricted distribution.
- Claiming that climographs show sharp boundaries between biomes; real boundaries change gradually.
- Assuming temperature and rainfall are the only factors that decide a biome; soil and grazing also matter.
- Mixing up the roles of the two partners: the algae photosynthesise and the polyp shelters them.
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